Wood planing machines or joiners have cutter heads for planing wood during finishing of the wood. Commonly, these planing machines have a plurality of rotary cutting heads, such as for planing the top, bottom and side surfaces of lumber. The cutter heads have knife blades releasably mounted thereto by a mounting mechanism. The present invention relates to improved cutter heads and improved mounting systems for mounting blades to cutter heads as well as to planing machines with such improvements and to related methods.
The present invention is not limited to any specific embodiment disclosed herein nor is it limited to embodiments which accomplish one or more advantages set forth herein. Instead, the invention is directed toward new and unobvious features and method acts, both alone and in combinations and sub-combinations with one another.
The cutting heads are typically cylindrical and may include projecting shafts for engagement by motors which drive the cutting heads in rotation to accomplish the cutting or planing task.
FIG. 1 schematically illustrates one form of a known rotary cutter head for use in a planer. The cutter head of FIG. 1 comprises an elongated cylindrical body 20 having a plurality of inwardly directed elongated slots, some of which are numbered as 21. A respective cutter blade is included in each of the slots. Several of these cutter blades are indicated at 22 in FIG. 1. The cutter head is rotated in the direction of arrow 26. The respective cutter blades shave wood chips from lumber (e.g., lumber 32 supported by a supporting surface 34) as the lumber is advanced in the direction of arrow 36 through the planer. Upper and lower cutter heads may oppose one another so that two opposing surfaces of the lumber are planed at the same time, although this is not required. The knife blades 22 each have a tapered surface 40 which terminate in a knife edge 42 which planes the lumber. The knife edges 42 are desirably positioned at a common radius R1 from the center 25 of the cutter body 20. Motors drive the cutter bodies at typically a very high speed, such as 3600 RPM, although this speed can be varied. The slots 21 are sized to each receive a blade retainer, such as a gib or clamping piece, some of which are indicated at 50 in FIG. 1. The illustrated gibs 50 each have a flat surface which bears against the adjacent side surface of the knife blade with the gib being positioned at the leading side of its associated knife blade relative to the direction of rotation. A concave surface may be formed at the outer exposed edge of the gib to assist in directing woodchips away from the cutter head during the planing operation. Some of these concave surfaces are indicated at 52 in FIG. 1.
The cutter body 20 is provided with a plurality of tapped counter bore holes, some of which are indicated at 54 in FIG. 1. A plurality of these bores 54 is associated with and positioned along the length of each blade. These holes each receive a set screw (some of which are indicated at 55 in FIG. 1) which applies a clamping force directly against the associated gib to urge the gib against the adjoining surface of the blade to clamp the blade in the slot at its desired position. In an exemplary prior art cutter head, the slots, blades and gibs are fifteen inches long. In addition, a number of set screw receiving holes (eight to ten, for example) are positioned at spaced apart locations in the cutter body along the length of each slot to receive set screws to bear against the gib when the gib and blade is positioned in the associated slot. Thus, for a 15″ wide cutter body, for example, eight to ten pressure application points are provided (one for each set screw) to clamp each gib and blade in the associated slot when the respective set screws are tightened within the bores associated with the gib.
As can be seen in FIG. 1, which illustrates a 14.25 inch diameter cutter head (2×R1=14.25 inches), 20 knives are positioned about the periphery of the cutter head with the knives being oriented at a 25 degree cutting angle. The positioning of the set screw receiving bores due to this construction limits the number of blades that can be included in such a cutter head because the bores occupy a significant portion of the space between the blades at the surface of the cutter head.
During normal use of a cutter head, the knife steel eventually becomes dull. It is common practice to resharpen the blades at this point using a method known as jointing. In one common approach, a sharpening stone is held perpendicular to the centerline of the cutter head with the machine running (e.g., the cutter head rotating at 3600 RPM) to resharpen the blades. Resharpening can be accomplished a number of times (for example, two to four times) until the surface at the point of the knife blade becomes too wide (also known as the “heel”) for effective cutting and it begins to beat the wood and create raised grain. When this occurs, the knife blades are removed and replaced with new or reground blades with the taper 40 and sharp tip 42. The removed knives may be reground numerous times until their width (the distance from the base of the blade to the tip) is reduced to a point where they are no longer considered safe. For example, a new knife may have a width of two inches and may be reground until the width is about 1 1/16 inches as an exemplary minimum. When this happens, the knife steel is discarded.
When the new blades are installed, they need to be set at the proper height so that the tips of the knives all lie on the same periphery, e.g., at R1 in FIG. 1. A common approach is to loosely mount the knives in the cutter head body and then to use either a hammer gauge or a roller gauge to set the knives to have tips at the same periphery.
One approach for setting blade height uses a hammer gauge. A hammer gauge is a hand held device consisting of a pair of contoured surfaces which make contact with the cutter head body on either side of a knife. A slot between the contoured surfaces fits over the sharpened edge of the knife with a recess to protect the knife edge from damage. In use, the knives are loosely set at a generous distance above (radially outwardly beyond) their intended final position. The slot of the hammer gauge is then placed over the knife at one end of its length and a hammer is used to lightly drive the hammer gauge and knife down into its slot in the cutter head body until the contoured portions of the gauge make contact with the cutter body. This is repeated at the other end of the knife. After the height of all of the knives have been set, the set screws are progressively tightened, alternating tightening between set screws for knives at 180 degrees apart about the head so as to reduce stresses on the cutter head body.
Another approach for setting blade height uses a roller gauge. A roller gauge is a fixture which is either permanently or temporarily attached to the planer machine in such a way as to accomplish the same result as the hammer gauge. In one form, a roller gauge consists of two side plates, each with a pivot point at one end and a bored hole at the other. The bored holes accept a shaft running between the side plates. The length of the shaft is sized to be compatible with the width of the cutter head involved. Two discs are mounted on the shaft. Each disc has a flat surface which has been machined from its periphery. The discs are free to rotate on the shaft. The fixture is pivoted so as to bring the discs to a specific distance from the cutter head axis. This distance is adjustable and will ultimately be the preferred distance for the edges of all the knives in the head. In use, the knives are again loosely set at a generous distance above their intended final position. This initial setting is done with the discs on the fixture set so that the flat portion of the disc is nearest the knife edges, but with clearance between the flat and the knife edge. The discs are then turned on their shaft so that the disc radius is closest to the knife edges and will create an interference condition between the two. The cutter head body is then gently rotated on its axis and as each knife edge makes contact with the two discs on the fixture, the knife is forced down into its respective slot in the cutter head body. In this manner, the edges of all the knives are set to the same radius on the head. The final procedure for tightening the knives into the head may be the same as described above for the hammer gauge process.
With the above approach, replacement of the knives is time consuming. This results in considerable downtime while the knives are being replaced. In addition, the point contact provided by the set screws against the gib requires a significant number of screws per length of gib to provide a given knife holding force. An increase in the number of screws that is required means that more screws need to be loosened and then re-tightened during knife blade replacement.